This invention is a surgical method and device for inserting a biocompatible material into an intrastromal passageway to permanently alter corneal curvature. The device and method allow for the placement of the material in the optimal position for maximal visual correction.
Anomalies in the overall shape of the eye can cause visual disorders. Hyperopia (xe2x80x9cfarsightednessxe2x80x9d) occurs when the front-to-back distance in the eyeball is too small. In such a case, parallel rays originating greater than 20 feet from the eye focus behind the retina. In contrast, when the front-to-back distance of the eyeball is too large, myopia (xe2x80x9cnearsightednessxe2x80x9d) occurs and the focus of parallel rays entering the eye occurs in from of the retina. Astigmatism is a condition which occurs when the parallel rays of light do not come to a single point within the eye, but rather have a variable focus due to the fact that the cornea is aspherical and refracts light in a different meridian at different distances. Some degree of astigmatism is normal, but where it is too high, it must often be corrected.
Hyperopia, myopia, and astigmatism are usually corrected by glasses or contact lenses. Surgical methods for the correction of such disorders are known. Such methods include radial keratotomy (see e.g., U.S. Pat. Nos. 4,815,463 and 4,688,570) and laser corneal ablation (see, e.g., U.S. Pat. No. 4,941,093).
Another method for correcting those disorders is through implantation of polymeric rings in the eye""s corneal stroma to change the curvature of the cornea. Previous work involving the implantation of polymethylmethacrylate (PMMA) rings, allograft corneal tissue, and hydrogels is well documented. One of the devices involves a ring design that allows a split ring to be inserted into a channel dissected in the stromal layer of the cornea using a minimally invasive incision through which the channel for the implant is created and through which the implant is inserted.
U.S. Pat. No. 4,452,235 to Reynolds describes a method and apparatus for corneal curvature adjustment. The method involves inserting one end of a split end adjusting ring into the cornea of the eye and moving the ring in a circular path until its ends meet. The ends are thereafter adjusted relative to each other until the shape of the eye has assumed a desired curvature whereupon the ends are fixedly attached to maintain the desired curvature of the cornea.
PCT Application No. PCT/US93/03214 filed Apr. 7, 1993 describes a corneal vacuum centering guide and dissector for use in inserting an intrastromal corneal ring (xe2x80x9cICRxe2x80x9d). The device is made of up of three major components: a vacuum centering guide, a barrel that fits within the inner bore of the centering guide and to which is attached the third major component, a circular dissecting ring. The three components are further described below.
The vacuum centering guide has a support base that has a proximal end, a distal end and a center section. The center section has a wall with a generally cylindrical bore with a central axis. The central section extends between the proximal and distal ends of the support base. The cylindrical bore has a ratio of length to diameter of between about 0.25:1 and 15:1. An annular vacuum chamber located at the proximal end of the support base is adapted to create an annular vacuum space when placed against the eye.
The barrel and dissector blade assembly is used in connection with the vacuum centering guide in order to produce the circular interlamellar pathway within the corneal stroma. The barrel fits within the inner bore of the centering guide. The dissecting ring is attached to the barrel in such a way that when an eye surgeon twists the barrel, the ring moves through the interlamellar space in the stroma producing the desired channel or pathway.
A drawback to prior methods to produce an intrastromal channel has been the inability to control the depth of the pathway since the dissector blade tended to create a nonplanar channel. A new method for producing a more planar channel is described herein.
The present invention provides for an improved method and device for producing a desired channel or pathway in the interlamellar space in the corneal stroma for inserting a biocompatible material to permanently alter corneal curvature.
In one aspect, the invention is a method for making a channel in corneal tissue to facilitate inserting a biocompatible material into the corneal stroma of an eye. The method involves (a) cutting a small incision into the corneal stroma; (b) inserting a clockwise or counter-clockwise dissector blade into the incision and rotating it clockwise or counter-clockwise to produce a clockwise or counter-clockwise channel; (c) inserting the other of the clockwise or counter-clockwise dissector blades into the incision and rotating it clockwise or counter-clockwise to produce a clockwise or counter-clockwise channel; and optionally (d) inserting a clockwise probe into the clockwise channel and a counterclockwise probe into the counterclockwise channel to see if the channels meet.
When the channels meet, the biocompatible material is inserted into the eye. When the channels do not meet, the method of the invention further involves (e) determining which of the clockwise or counterclockwise channels is the lower channel by overlaying the probe tips and observing the probes; (f) removing the probes; (g) inserting a clockwise or counter-clockwise channel connector into the lower channel depending on whether the lower channel is the clockwise or counter-clockwise channel and rotating it clockwise or counterclockwise or until the dissector is observed to break through into the upper channel; and (h) removing the dissector by rotating it in the opposite direction. If the breakthrough into the upper channel has occured, the biocompatible material is inserted into the eye.
If, however, the channels still do not meet, the method of the invention further involves: (i) inserting a clockwise or counter-clockwise finish channel connector into the lower channel depending on whether the lower channel is the clockwise or counter-clockwise channel and rotating it clockwise or counterclockwise until the channels meet or until the finish channel connecting instrument rotates around to the entry incision; and (j) removing the finish channel connector by rotating it in the opposite position. The biocompatible material is then inserted into the eye.
In another aspect, the invention is a kit useful for inserting an intrastromal corneal ring or other biocompatible material into the corneal stroma of an eye. The kit comprises: (a) a clockwise dissector; (b) a counter-clockwise dissector; (c) a clockwise channel connector; (d) a counter-clockwise channel connector; (e) a clockwise finish channel connector; (f) a counter-clockwise finish channel connector; (g) a clockwise probe; and (h) a counter-clockwise probe.